From afar, the largest planet in the solar system is a swirl of brown, yellow and white clouds, topped off with a distinctive red blemish, the mark of a raging 300-year-old storm that would smother the Earth many times over.

Jupiter is a gas giant and, after the Sun, the most massive object in the solar system. The planet spins fast, making a day last only 10 hours and the equator bulge out to a diameter of 89,000 miles. All the planets in the solar system, or more than 1,300 Earths, would fit inside the space Jupiter occupies.

Jupiter is a distant planet, more than five times further from the sun than Earth. The orbit takes Jupiter 12 Earth years to complete.

Like all gas giants, Jupiter has no surface in the conventional sense, but the top of the cloud deck writhes with storms and hurricanes.

If a person could stand on the top of Jupiter's clouds, they would feel more than twice the gravitational pull of Earth. A person who weighed 80kg on our home planet would weigh nearly 200kg. High up the temperature is close to -145C (-229F), but near the centre this rises to 24,000C (43,232F), hotter than the surface of the sun.

The outer clouds are about 90% hydrogen and 10% helium, but further in the planet becomes richer in helium and the heavier elements. At the heart may be a rocky core.

The planet becomes denser and hotter deeper in as the pressure soars. The clouds thicken, then droplets begin to appear and, deeper than 600 miles, all gas is turned to liquid.

Even deeper, electrons are squeezed off hydrogen atoms to produce a substance never seen on Earth. Under such extreme conditions, the hydrogen behaves like liquid metal, conducting electricity as well as heat. The metallic hydrogen sea is tens of thousands of miles deep.